1. Field of the Invention
The present invention relates to a PWM power amplifier and a method for controlling the same, which are desirably employed in an audio instrument such as a Compact Disc (CD) player.
2. Description of the Related Art
In the past, in a CD player of this type, after performing the Pulse Width Modulation (PWM) processing for an audio signal reproduced from a CD, a PWM power amplifier amplifies thus obtained PWM signal based on a power voltage supplied from a household power source to send a power of thus amplified signal to a speaker (for example, refer to Japanese Utility Model Laid-Open Publication No. 5-70017).
FIG. 1 shows a block diagram of a PWM power amplifier that has been known in the art (for example, refer to Japanese Utility Model Laid-Open Publication No. 5-70017). In the PWM power amplifier 1, a PWM signal S1 that is an input digital audio signal is converted to a signal of a predetermined format by a format conversion unit 2, and thus converted signal is sent to a processor 3.
The processor 3 divides a PWM signal S1′ into a positive side signal S2A and a negative side signal S2B, and sends thus divided respective signals to a power output unit 5.
The power output unit 5 is of the Baranced Transformerless (BTL) connection configuration, which power-amplifies the positive side signal S2A and negative side signal S2B sent from the processor 3 using a Direct Current (DC) voltage supplied from a power source 6, and sends thus amplified signals to a speaker 8 through a pair of Low Pass Filters's (LPF) 7A, 7B, composed of coils L7A, L7B and capacitors C7A, C7B, for removing high frequency signal components.
The power source 6 converts an Alternating Current (AC) voltage supplied from a household power source, not shown, arranged at the outside to a DC voltage, and adjusts the voltage level of the DC voltage to be supplied to the power output unit 5 based on a volume value adjusted under the operation of the user.